Effect of Cr₂O₃ addition on microstructural evolution and mechanical properties of Al₂O₃

The effects of chromia (Cr₂O₃) additions on the microstructural evolution and the mechanical properties of alumina (Al₂O₃) were investigated. When small amounts (<5 mol%) of Cr₂O₃ were added in samples hot pressed at 1500°C, the grain size distribution became bimodal; large platelike grains were dispersed in a relatively small grained matrix. The large grains were composed of a core region that is free of Cr and a surrounding shell region rich in Cr. The interface between the core and the shell was composed of misfit dislocations. The high diffusion rate of Cr ions through the surface of alumina was attributed to this microstructural evolution. The mechanical properties of the specimens were strongly influenced by this microstructural change. The fracture toughness and the flaw tolerance (R-curve behavior) of Al₂O₃ were improved markedly by the formation of the large platelike grains. The hardness and the elastic modulus also increased, however, the fracture strength decreased by the addition of Cr₂O₃.